Molecular Architectures of Trimeric SIV and HIV-1 Envelope Glycoproteins on Intact Viruses: Strain-Dependent Variation in Quaternary Structure
Figure 5
Closed and open states of trimeric SIV Env.
(a, b) Top views of the density maps of (a) closed (SIVmneE11S) and (b) open (SIV CP-MAC) states fitted with gp120 coordinates. The missing V1/V2 loop is represented by the red sphere to highlight the dramatic difference in location of the loop between the two states. (c, d) Top view of the molecular surfaces of gp120 trimers in (c) closed (SIVmneE11S) and (d) open (SIV CP-MAC) states, highlighting selected residues (216–220, 262, shown in blue) that are conserved across most SIV and HIV-1 Env sequences, which are buried in the closed state, but exposed in the open state. Residues in the CD4 binding site and in the stem of the V1/V2 and V3 loops are shown in yellow, red and green, respectively. The coordinate system in each panel provides an aid to visualizing the rotation of each gp120 monomer in the transition from the closed to open state. Filled dark triangle indicates location of the 3-fold symmetry axis.